This application claims the benefit of Korean Patent Application No. 2000-5074 filed on Feb. 2, 2000, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) panel, and more particularly, to a liquid crystal display panel and a method of fabricating the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for reducing an injection time in injecting a liquid crystal into the liquid crystal display panel.
2. Discussion of the Related Art
A typical liquid crystal display (LCD) panel has upper and lower substrates and an interposed liquid crystal layer. The upper substrate usually includes common electrodes while the lower substrate includes pixel electrodes and switching elements, such as thin film transistors (TFTs). Since the present invention relates to manufacturing a liquid crystal display device, a brief description regarding the conventional liquid crystal display manufacturing processes will be helpful to fully understand the present invention. Common electrodes and pixel electrodes are formed on upper and lower substrates, respectively. A seal is then formed on the lower substrate. The upper and lower substrates are then bonded together using a sealing material such that the common electrodes of the upper substrate and the pixel electrodes of the lower substrate face against each other. Thus, a liquid crystal cell is formed therein. A liquid crystal material is then injected into the cell through injection holes. The injection holes are then sealed. Finally, polarizing films are attached to the outer surfaces of the upper and lower substrates.
In operation, the light passing through the liquid crystal cells is controlled by electric fields that are applied through the pixel and common electrodes. By controlling the electric fields, desired characters or images can be displayed on the panel.
While fabricating various components for a liquid crystal display, such as thin film transistors or color filters, typically require numerous manufacturing steps, the overall fabrication process is relatively straightforward. FIG. 1 illustrates a typical liquid crystal cell manufacturing process. In the initial step (st1), an array of thin film transistors and pixel electrodes are formed over an array or TFT substrate (rear substrate).
The next step (st2) forms an orientation film over the lower substrate. This includes the processes of depositing a polymer thin film over the lower substrate and then uniformly rubbing the polymer thin film with a fabric. The rubbing process involves rubbing the surface of the polymer thin film so as to orient or align the film. A typical orientation film is an organic thin film such as a polyimide thin film.
The third step (st3) produces a seal pattern on the lower substrate. When the upper and lower substrates are attached, the seal patterns form a cell gap that will receive a liquid crystal material. The seal pattern will also prevents the interposed liquid crystal material from leaking out of the completed liquid crystal cell. A thermosetting resin and a screen-print technology are conventionally used to form the seal pattern.
In the fourth step (st4), spacers are sprayed over the lower substrate. The spacers have a predetermined size and act to maintain a precise and uniform space between the upper and lower substrates. Accordingly, the spacers are placed with a uniform density on the lower substrate using either a wet spray method or a dry spray method. In the wet spray method, the spacers are mixed in an alcohol and sprayed on the substrates. The dry spray method includes only the step of spraying a spacer. The dry spray method is further classified into a static electric spray method using static electricity and a non-electric spray method utilizing a gas pressure. Since a static electricity can be harmful to the liquid crystal, the non-electric spray method is more widely used in fabricating the LCD panel.
The next step (st5) aligns and attaches the color filter substrate (or upper substrate) and the TFT substrate (or lower substrate) together. An aligning margin should be less than a few micrometers. If the upper and lower substrates are aligned and attached with a margin greater than the aligning margin, a display quality is deteriorated by light leakage during the operation of the liquid crystal display panel.
In the sixth step (st6), the liquid crystal cells fabricated in the previous five steps are cut into an individual liquid crystal cell. Conventionally, a liquid crystal material was injected into the space between the upper and lower substrates before the substrates were cut into the individual liquid crystal cell. As a display size becomes larger, a liquid crystal material is infected into the cell after the liquid crystal display panel is cut into a unit cell. The processes of cutting the cells typically includes the step of scribing using a diamond pen to form cutting lines on the substrate, and the step of breaking separates the substrate along the scribed lines.
In the seventh step (st7), a liquid crystal material is infected into the individual liquid crystal cells. Since each individual liquid crystal cell occupies hundred square centimeters in area while it has only a few micrometer gap between the substrates, a vacuum injection method is effectively and widely used in injecting a liquid crystal. Generally, injecting a liquid crystal material into the cells takes the longest manufacturing time in the fabrication process. Thus, for manufacturing efficiency, it is important to have optimum conditions for a vacuum injection.
FIG. 2 shows a conventional vacuum injection process for injecting a liquid crystal material into the liquid crystal cell. To inject the liquid crystal material, a liquid crystal cell 2 having an injection hole 4 is placed inside a vacuum apparatus 6. The liquid crystal cell is located over a vessel 8 that contains the liquid crystal material 10. During operation, a suction process removes air from the vacuum apparatus 6 to create a vacuum condition.
In practice, it is possible to add small air bubbles in the liquid crystal material 10 to form larger air bubbles. However, such air bubbles can cause problems. Accordingly, before injection, the liquid crystal material 10 should be left under a vacuum condition of a few mTorr for a sufficient time so that the air bubbles in the liquid crystal material 10 are removed. Conventionally, the vessel 8 containing the liquid crystal material 10 and the liquid crystal cell 2 are left under this vacuum condition.
One method of injecting the liquid crystal material into the liquid crystal cell is to dip the liquid crystal cell into the tray containing the liquid crystal material. However, the dipping method consumes too much of the liquid crystal material. Another method includes touching (i.e., slightly dipping) only the injection hole 4 to the liquid crystal material. The touching method as shown in FIG. 2, after the air in the liquid crystal cell 2 and the liquid crystal material 10 is removed, the injection hole 4 is slightly dipped into the vessel 8 containing the liquid crystal material 10. At first, the liquid crystal material 10 is injected into the liquid crystal cell 2 by capillary forces. Thereafter, a nitrogen gas is introduced into the vacuum apparatus 6. A difference in pressure between the interior and exterior of the liquid crystal cell 2 forces liquid crystal material 10 into the liquid crystal cell 2.
FIG. 3 is a graph illustrating the pressure in the vacuum apparatus 6 with respect to time. During the period xe2x80x9cAxe2x80x9d, a vacuum condition is generated. At the end of the period xe2x80x9cAxe2x80x9d the injection hole 4 is dipped into the vessel 8 containing the liquid crystal material 10. During the period xe2x80x9cBxe2x80x9d, the liquid crystal material 10 is injected into the liquid crystal cell by a pressure difference. After the injection of the liquid crystal material is complete, the injection hole 4 is sealed with an epoxy-based sealant that is applied through a dispenser.
The liquid crystal used in the fabrication of the above-mentioned LC cell is usually a twisted nematic (TN) liquid crystal because the TN liquid crystal is easily controllable and provides a good picture quality. However, since the TN liquid crystal has a long response time, a moving image cannot be readily displayed. Moreover, a residual image may be formed in large LCD devices, such as greater than 20 inches. As a result, a picture quality decreases. Thus, there is a trend to replace the TN liquid crystal with other types of liquid crystal in the large LCD device for a better displaying image.
Meanwhile, a ferroelectric liquid crystal (FLC) and an anti-ferroelectric liquid crystal (AFLC) have lately drawn an attention as a substitute for the TN liquid crystal because the FLC and the AFLC have a large spontaneous polarization characteristic. Also, the AFLC is bistable. When the AFLC is used for an LCD device, a contrast is not deteriorated with an increase in the number of pixel. In addition, a flicker is suppressed. The AFLC has a response time a hundred times faster than the TN liquid crystal and a super twisted nematic (STN) liquid crystal. This is because the AFLC has a spontaneous polarization characteristic that leads to a high-speed response, thereby improving moving images in displaying. In other words, a short response time prevents a residual image, and improves a mouse control of the computer, MS window program control, and moving images in displaying. Moreover, the AFLC molecules have an advantage of a wide viewing angle in the large LCD device due to its spatial re-arrangement with respect to the applied voltage.
However, a cell gap between the upper and lower substrates should be maintained by the distance of less than 2 xcexcm in order to apply the AFLC to the LCD device in realizing the bistability. However, it is well known that a liquid crystal cell is impossible to have a uniform cell gap of less 2 xcexcm.
FIG. 4 is a schematic cross-sectional view of a typical LCD panel. As shown in the drawing, a LCD cell includes a lower and upper substrates 1 and 11, and an interposed liquid crystal material 10. A pixel electrode 3 is formed on the lower substrate 1 and a common electrode 12 is formed on the upper substrate 11. The lower substrate 1 and the upper substrate 11 are spaced apart by the distance xe2x80x9cdxe2x80x9d of about 4 to 5 xcexcm (i.e. a cell gap)
In the conventional method of injecting the liquid crystal material, as described above, the vacuum infection method is employed after attaching and aligning the array substrate (lower substrate) 1 and the color filter substrate (upper substrate) 11. However, it takes too much time to inject the liquid crystal material into the LCD cell larger than 20 inches. On the other hand, an LCD cell less than 20 inches can be injected with the liquid crystal material in a short period of the time.
Meanwhile, the large LCD panel needs a fast response time in order to improve a display quality for moving images and to decrease a residual image. Therefore, the AFLC is used for the large LCD device and a liquid crystal is injected into the cell gap of less than 2 xcexcm to achieve the fast response time. However, it takes too much time to inject the AFLC uniformly into this cell gap. Moreover, since a viscosity coefficient of the AFLC is ten times higher than that of the TN liquid crystal, an injection time becomes longer. For example, coefficient of the TN liquid crystal is 20 mm2/sec.
Accordingly, the present invention is directed to a liquid crystal display panel that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to decrease an injection time of the liquid crystal and to increase yield of the liquid crystal display panel.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
The present invention provides a liquid crystal device, which includes a liquid crystal display includes first and second substrates, a light-transmitting portion in the first and second substrates, wherein the light-transmitting portion has a first cell gap, a light-shielding portion in the first and second substrates, wherein the light-shielding portion has a second cell gap, wherein the second cell gap is larger than the first cell gap, and a liquid crystal layer between the first and second substrates.
In another aspect the present invention, a liquid crystal display includes first and second substrates positioned to have a first cell cap, a first hole in close proximity of the first substrate, a second hole in close proximity of the second substrate, wherein the first and second holes broaden the first cell gap, thereby forming a second cell gap; and a liquid crystal layer between the first and second substrates.
A further aspect of the present invention, a method of fabricating of a liquid crystal display having first and second substrates, the method includes the steps of forming a light-transmitting portion in the first and second substrates, wherein the light-transmitting portion has a first cell gap, forming a light-shielding portion in the first and second substrates, wherein the light-shielding portion has a second cell gap larger than the first cell gap, and forming a liquid crystal layer between the first and second substrates.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.